def is_prime(n):#判断质数
    """
    to check if a number is prime or not
    """
    if n < 2:
        return False
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:
            return False
    return True

print(is_prime(13))

def factorial(n):
    if n== 1:
        return 1
    else:
        return n * factorial(n-1)

